[clang] [llvm] Add support for flag output operand "=@cc" for SystemZ. (PR #125970)

[Ulrich Weigand via cfe-commits]

https://github.com/uweigand commented:

Not a full review, just some initial comments on combineCCMask.   I think it would be good to have more comments explaining the specific transformations you're attempting to implement, with an argument why they are correct for all inputs.

https://github.com/llvm/llvm-project/pull/125970